Emission control system and a method for operating an emission control system

ABSTRACT

In an emission control system that includes a particle filter, an arrangement is provided upstream of the particle filter, the arrangement being configured to prevent the development of ash-forming compounds of sulfur in the exhaust. The emission control system may be used with a diesel engine.

FIELD OF THE INVENTION

[0001] The present invention relates to an emission control system,particularly for an automobile with an internal combustion engine,having a particle filter. The present invention also relates to a methodfor operating an emission control system.

BACKGROUND INFORMATION

[0002] Particle filters are used for diesel-operated vehicles to reduceparticle emissions. Particle filters are primarily used to capture sootparticles in the exhaust. Soot particles captured in the particle filtercan be combusted in special operating phases of the internal combustionengine. However, ash residue in the filter cannot be combusted, whichclogs the filter over the life of the vehicle.

[0003] The following ash components are generally responsible forclogging the filter: motor oil ash residue from the oil consumed by theinternal combustion engine; fuel ash residue from fuel consumption;additive ash residue from fuel additives to help regenerate the particlefilter; and other residue, e.g., from intake air, motor abrasion orwear, and corrosion of the exhaust system.

[0004] As a result, particle filters must be replaced or cleaned in awashing procedure after a given service interval, e.g., every 80,000 kmtraveled.

[0005] The clogging of the filter from ash is a continuous process overthe life of the vehicle. With an average oil consumption of 0.2 1/1000km, up to 180 grams ash or more can develop after 100,000 km. The ashresidue in the filter causes increased pressure drop in the particlefilter, which increases exhaust counterpressure, increases fuelconsumption by 8% or more, and decreases engine power. Since the ashresidue cannot be decomposed or regenerated, the particle filter must beeither removed and cleaned or replaced after a certain period or after acertain amount of ash has collected in the filter.

[0006] In particular, Ca, Fe, Mg, Zn, P and S develop in the exhaustfrom oil consumption. Sulfur develops in the exhaust from fuelconsumption. Ce, Fe, Ca and Na enter the exhaust from fuel additives. Feand Al enter the exhaust from abrasion and corrosion.

[0007] Ash forms from sulfates, oxides and phosphates, e.g., sulfate ashin the form of CaSO₄ and oxide ash in the form of CaO.

[0008] More than 50% of the resulting ash deposits in the filter arecreated by sulfate ash.

[0009]FIG. 5 schematically illustrates a conventional emission controlsystem with oxidation catalyst 1 and particle filter 2. The exhaustcoming from the engine contains sulfur compounds, e.g., 98% SO₂, 2% SO₃and Ca, Fe, Mg, Zn and P. At temperatures above 350° C., sulfate formsin oxidation catalyst 1, where SO₂ and SO₃ are converted into SO₄. Ash,such as CaSO₄, ZNSO₄, MgSO₄, CaO, FeO, etc., develops downstream fromoxidation catalyst 1. This ash collects in particle filter 2 and clogsit.

SUMMARY

[0010] The present invention provides an emission control system and amethod to operate an emission control system to reduce the clogging ofthe particle filter by ash residue.

[0011] According to the present invention, an emission control system,particularly for a motor vehicle having an internal combustion engine,is provided with a particle filter, and an arrangement is providedupstream from the particle filter to prevent ash-forming compounds ofthe sulfur in the exhaust from developing.

[0012] The present invention is based on the principle of preventing ashfrom developing in advance of the particle filter and transforming thecompounds responsible for the ash formation into a gaseous state orkeeping them in a gaseous state so that they can flow through theparticle filter without collecting. The objective is to avoid primarilysulfates, which represent a major component of the ash.

[0013] Accordingly, the sulfur in the exhaust, which is primarilyresponsible for the formation of ash, is converted into compounds thatdo not form ash in order to prevent sulfates from forming in theexhaust.

[0014] In one example embodiment of the present invention, thearrangement includes an SO_(x) collector.

[0015] By using an SO_(x) trap or SO_(x) collector, the sulfur containedin the exhaust may be stored to substantially reduce the amount ofash-forming sulfur compounds in the exhaust. When the storage capacityof the SO_(x) trap is exhausted, it may be regenerated in a regenerationphase. The stored sulfur is released in the form of gaseous compoundsthat may pass through the particle filter.

[0016] The arrangement may be combined with a NO_(x) collector and/or anoxidation catalyst.

[0017] These measures improve the quality of the exhaust.

[0018] The present invention also provides a method to operate anemission control system so that no ash-forming compounds develop fromthe sulfur contained in the exhaust.

[0019] The formation of ash may be substantially reduced in this manner,since sulfur compounds represent a large portion of the compoundsresponsible for ash formation.

[0020] In a further example embodiment of the present invention, thereare normal operating phases with a lean exhaust composition for storingthe sulfur contained in the exhaust, and there are regeneration phaseswith a rich exhaust composition to release the stored sulfur in the formof gaseous compounds.

[0021] During the normal operation phases, the formation of sulfate inthe exhaust and accordingly the formation of sulfate ash are reduced.When the storage capacity of the sulfur collector is exhausted, aregeneration phase with a rich exhaust composition is initiated toregenerate the sulfur collector. The stored sulfur is released in theform of gaseous compounds that may pass through the particle filter.

[0022] This arrangement effectively prevents the filter from cloggingdue to ash. The service interval for cleaning or replacing a particlefilter may be greatly increased with the same filter volume. The sulfuroxides in the exhaust, such as SO₂ and SO₃, are stored in the sulfurcollector on a storage metal such as barium (Ba) . Hence, BaSO₄ developsin the sulfur collector. This arrangement prevents the formation ofsulfate in the exhaust downstream from the sulfur collector. During theregeneration phase, the BaSO₄ stored in the sulfur collector isconverted to SO₂, H₂S and COS. There is little formation of SO₄ due tothe low-oxygen or rich exhaust composition. The released sulfurcompounds are gaseous and may therefore pass through the particlefilter. After the sulfur collector is regenerated, the engine may beoperated with a lean exhaust composition.

[0023] The exhaust temperature in the regeneration phase may be raisedto 550-700° C.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a schematic view of a first example embodiment of theemission control system according to the present invention.

[0025]FIG. 2 is a schematic view of a second example embodiment of theemission control system according to the present invention.

[0026]FIG. 3 is a schematic view of a third example embodiment of theemission control system according to the present invention.

[0027]FIG. 4 is a schematic view of an exhaust system of an automobilewith an internal combustion engine having an emission control systemaccording to the present invention.

[0028]FIG. 5 is a schematic view of a conventional emission controlsystem.

DETAILED DESCRIPTION

[0029]FIG. 1 schematically illustrates an emission control systemaccording to the present invention with a SO_(x) collector 10 andparticle filter 12. The exhaust passes via a pipe section 14 from aninternal combustion engine to SO_(x) collector 10. The direction of flowin the emission control system is indicated by arrows. The sulfurcompounds in the exhaust coming from the motor in pipe section 14 areapproximately 98% SO₂ and approximately 2% SO₃. Ca, Fe, Mg, Zn and P arealso contained in the exhaust.

[0030] SO_(x) collector 10 stores the sulfur oxides SO₂, SO₃ on astorage metal such as barium (Ba) when the exhaust composition is lean,a so-called hyperstoichiometric exhaust composition with λ>1, in theform of BaSO₄. The formation of sulfate in the exhaust and subsequentformation of sulfate ash are accordingly reduced. The ash-formingcomponents in the exhaust either react to form oxide ash or remain in agaseous state. For example, Ca, Fe, Mg, Zn and P are present in pipesection 16 and particle filter 12 as gaseous compounds and may passthrough them, which reduces the deposition of ash in the particle filter12. Even when oxide ash forms instead of sulfate ash, the amount of ashin particle filter 12 may be reduced, since oxide ash has a lower molarmass than sulfate ash.

[0031] The internal combustion engine creating the exhaust may beoperated with fuel containing less sulfur, e.g., less than 10 ppm, sothat there will be a very small base load of sulfur in the exhaust. Evenwhen sulfur-free fuel is used, SO_(x) collector 10 is useful since theexhaust in pipe section 14 contains sulfur components from consumedmotor oil.

[0032] When the storage capacity of SO_(x) collector 10 is exhausted, aregeneration phase according to the present invention is started. Theexhaust temperature is increased to 550-700° C. to regenerate ordesulfurize the collector, and the internal combustion engine isswitched to hypostoichiometric operation or rich operation (λ<1). In theregeneration phase, SO_(x) collector 10 releases the sulfur, stored asBaSO₄ in the form of gaseous sulfur compounds such as SO₃, SO₂, H₂S orCOS. There is little SO₄ formation due to the low-oxygen or richair/fuel ratio. The released sulfur compounds may pass through particlefilter 12 in a gaseous state. Even in the regeneration phase, sulfatesdo not form in pipe section 16, and Ca, Fe, Mg, Zn, P are present asgaseous compounds and may pass through particle filter 12 so that thereis less ash deposition. After SO_(x) collector 10 is regenerated, theinternal combustion engine may be operated with a hyperstoichiometric orlean exhaust composition.

[0033]FIG. 2 schematically illustrates another example embodiment of theemission control system according to the present invention in which, incontrast to the emission control system illustrated in FIG. 1, SO_(x)collector 10 is combined with NO_(x) collector 20.

[0034]FIG. 3 illustrates a third example embodiment of the emissioncontrol system according to the present invention in which, in contrastto the emission control system illustrated in FIG. 1, SO_(x) collector10 is combined with NO_(x) collector 20 and an oxidation catalyst 22.

[0035] The emission control systems illustrated in FIGS. 2 and furtherreduce pollutants in the exhaust. The emission control systemsillustrated in FIGS. 2 and 3 are operated in the same manner as thatillustrated in FIG. 1, i.e., with normal operation phases having leanexhaust composition to store the sulfur in the exhaust in the form ofsulfate, and, after the storage capacity of SO_(x) collector 10 isexhausted, with regeneration phases having a rich exhaust composition torelease the stored sulfur in the form of gaseous compounds.

[0036]FIG. 4 schematically illustrates a diesel engine 24 that includesan emission purification system according to the present invention.Diesel engine 24 is supplied with diesel fuel having a reduced sulfurcontent from a fuel tank 26. The fuel is injected with a so-calledcommon-rail injection system 28. Diesel engine 24 is provided with anexhaust turbocharger 30 that supplies compressed intake air viacharge-air cooler 32 to intake manifold 34 of diesel engine 24.

[0037] Between exhaust manifold 36 and intake manifold 34 is an exhaustreturn line 38 that may be opened and closed by controllable exhaustreturn valve 40.

[0038] Proceeding from the exhaust manifold 36, the exhaust from dieselengine 24 passes via the exhaust turbine of exhaust turbocharger 30 to aSO_(x) collector 42. SO_(x) collector 42 is combined with a NO_(x)collector and an oxidation catalyst. Downstream from SO_(x) collector 42is a particle filter 44. The particle filter 44 is followed by anunderbody catalyst that further reduces pollutant emissions. Downstreamfrom the underbody catalyst is a muffler to reduce noise.

[0039] Controller 50 controls common rail injection system 28 andexhaust turbocharger 30 and may accordingly set a rich or lean exhaustcomposition. Exhaust return valve 40 is also controlled by controller50. Sensors 52 are provided at several locations in the exhaust systemthat detect the current exhaust composition and send it to thecontroller 50.

[0040] By analysis of the sensor signals in controller 50, the remainingstorage capacity of SO_(x) collector 42, for example, may be inferred.If controller 50 determines that SO_(x) collector 42 is full, aregeneration phase is started. After SO_(x) collector 42 is regenerated,the controller 50 switches back to storage operation.

What is claimed is:
 1. An emission control system, comprising: aparticle filter; and an arrangement disposed upstream from the particlefilter, the arrangement being configured to prevent development ofash-forming compounds of sulfur contained in an exhaust gas.
 2. Theemission control system according to claim 1, wherein the emissioncontrol system is configured for use with an internal combustion engine.3. The emission control system according to claim 1, wherein thearrangement includes a SO_(x) collector.
 4. The emission control systemaccording to claim 1, wherein the arrangement includes a NO_(x)collector.
 5. The emission control system according to claim 3, whereinthe arrangement includes a NO_(x) collector.
 6. The emission controlsystem according to claim 1, wherein the arrangement includes anoxidation catalyst.
 7. The emission control system according to claim 3,wherein the arrangement includes an oxidation catalyst.
 8. The emissioncontrol system according to claim 5, wherein the arrangement includes anoxidation catalyst.
 9. A method for operating an emission controlsystem, the emission control system including a particle filter and anarrangement disposed upstream from the particle filter, the arrangementbeing configured to prevent development of ash-forming compounds ofsulfur contained in an exhaust gas, the method comprising the step of:preventing development of ash-forming compounds of sulfur contained inthe exhaust gas.
 10. The method according to claim 9, further comprisingthe steps of: operating the emission control system in a normaloperating phase with a lean exhaust composition to store sulfurcontained in the exhaust gas; and operating the emission control systemin a regeneration phase with a rich exhaust composition to releasestored sulfur as at least one gaseous compound.
 11. The method accordingto claim 10, wherein the step of operating the emission control systemin the regeneration phase includes the substep of raising an exhausttemperature to between 550° C. and 700° C.
 12. A method for reducing ashcomponents in a particle filter of an exhaust system for a dieselengine, comprising the steps of: maintaining ash-forming exhaustcomponents in a gaseous state in a catalyst disposed upstream from theparticle filter; storing sulfur in the catalyst; and passing theash-forming exhaust components in the gaseous state through the particlefilter.
 13. A device for reducing ash components in a particle filter ofan exhaust system of a diesel engine, comprising: a catalyst disposedupstream from the particle filter, the catalyst including asulfur-storing catalyst configured as a NO_(x) collector, the catalystbeing further configured to change ash-forming exhaust components to agaseous state flowable through the particle filter.